These new CPUs are pin compatible with the existing chips, almost $2 (US) cheaper, and have internal oscillators factory tuned to be accurate enough for USB full speed operation. This eliminates the need for an external crystal circuit including two associated capacitors bringing more than $1 (US) cost savings.

Thanks to Dangerous Prototypes for bringing the news of these new MCUs to my attention. And to Microchip for providing samples so quickly. Some stock of these 5V SPDIP chips is currently available directly from Microchip and more supply will be available in the coming months.